Catalysts containing a platinum group metal and produced in a sol-gel method, as well as a method for producing diarylcarbonates

ABSTRACT

Described is a process for preparing an aromatic carbonate, e.g., diphenyhl carbonate, in which an aromatic hydroxy compound, e.g., phenol, is reacted with carbon monoxide and oxygen in the resence of a supported catalst prepared by a sol-gel process, a quatermary ammonium or phosphonium salt and a base. The sol-gel supported catlyst comprises: (i) a first metal oxide selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and mixtures thereof; (ii) a second metal oxide selected from the group consisting of oxides of the elements of groups 4, 5, 6, 7, 11, 12, 13, 14, the iron group (atomic numbers 26 to 28), the rare-earth metals (atomic numbers 58 to 71) and mixtures thereof; and (iii) a metal selected from the group consisting of platinum metals, compounds of platinum metals (atomic numbers 44 to 46 and 77 and 78) and mixtures thereof. The sol-gel supported catlyst is aged, dried and optionally annealed prior to use in the process of the present invention.

This application is a 371 of PCT/EP98/04862 filed Aug. 5, 1998.

The present invention relates to platinum metal-containing mixed oxidecatalysts which have been prepared in a sol-gel process and their use ina process for preparing diaryl carbonates by reacting aromatic hydroxycompounds with carbon monoxide and oxygen.

It is known that organic carbonates can be prepared by oxidativereaction of aromatic hydroxy compounds with carbon monoxide in thepresence of a noble metal catalyst (DE-OS 28 15 512). Palladium ispreferably used as the noble metal. In addition a co-catalyst (e.g.manganese or cobalt salts), a base, a quaternary salt, a variety ofquinones or hydroquinones and a drying agent may also be used. Theprocedure may be performed in a solvent, preferably in methylenechloride.

In order to perform this process in an economic manner, effectiverecovery of the noble metal catalyst is a critical factor, in additionto the activity and selectivity of the catalyst. On the one hand thenoble metal catalyst represents a large cost factor. Losses of noblemetal catalyst have to be replaced at great cost. On the other hand noresidues of the noble metal catalyst should remain in the product. Theeconomic and efficient recovery of homogeneous catalysts for the processof oxidative carbonylation of aromatic hydroxy compounds to give diarylcarbonates has not hitherto been described. The separation of a noblemetal catalyst from a liquid reaction mixture, e.g. by filtering orcentrifuging, can be performed at low cost if heterogeneous supportedcatalysts are used.

In EP-A 572 980, EP-A 503 581 and EP-A 614 876 noble metal supportedcatalysts are used which contain 5% palladium on carbon supports.However, these types of supported catalysts produce only veryunsatisfactory conversions or even none at all, so that these are alsounsuitable for an economically viable process.

JP-A 01/165 551 (cited in accordance with C.A. 112:76618j (1990))describes using palladium or palladium compounds such as palladiumacetylacetonate, in combination with alkali metal or alkaline earthmetal iodides or ‘onium’ iodides, such as tetrabutylammonium iodide, andat least one zeolite to prepare aromatic carbonates.

JP-A 04/257 546 and JP-A 04/261 142 each describe an example of asupported catalyst for preparing aromatic carbonates in which siliconcarbide granules are used as the support material for a supportedcatalyst in a distillation column. Although drastic conditions (highpressure, high temperature) are used in the relevant examples, thesecatalysts produce only very low space-time yields. These low space-timeyields make the economic production of aromatic carbonates with thistype of supported catalyst impossible.

EP-A 736 324 describes the preparation of diaryl carbonates withheterogeneous catalysts which contain a platinum metal, preferablypalladium, and a co-catalytic metal compound, preferably a metal fromthe group Mn, Cu, Co, Ce and Mo. When preparing the catalysts theco-catalytic metals are applied to a support.

EP-A 736 325 describes the preparation of diaryl carbonates withheterogeneous catalysts which contain a platinum metal, preferablypalladium, on a support which consists of a metal oxide in which themetal may exist in several valency states.

Although these supported catalysts enable the preparation of aromaticcarbonates for the first time, a further increase in activity isdesirable from an economic point of view.

It has now been found that higher catalyst activities can be obtained ifmixed oxides e.g. of V, Mn, Ti, Cu, La, the rare-earth metals andmixtures thereof which have been prepared in a sol-gel process and whichcontain platinum metals are used a catalysts.

The invention provides catalysts which contain

(i) an oxide of the elements silicon, aluminium, titanium, zirconium ora mixture of oxides of these elements,

(ii) one or more co-catalytic metal oxides from groups 4, 5, 6, 7, 11,12, 13, 14, the iron group (atomic numbers 26 to 28) or the rare-earthmetals (atomic numbers 58 to 71) in the periodic system of the elementsin accordance with the new IUPAC nomenclature, and

(iii) one or more platinum metals or one or more compounds of platinummetals (atomic numbers 44 to 46 and 77 and 78) in an amount 0.01 to 15wt. %, calculated as platinum metal and with respect to the total weightof catalyst,

which are obtained by preparing a gel from one or more suitableprecursor(s) of the components mentioned under (i) and (ii) and theplatinum metal component (iii), ageing, drying and optionally annealingthe gel.

The gel according to the invention can be prepared by almost any knownmethod. Methods which are known for preparing mixed oxides based on agel are preferably used. This includes, for example, the hydrolysis ofone or more metal alkoxides and/or hydrolysable metal compounds underacid, neutral or basic conditions in suitable solvents at temperaturesof 0° C. to 200° C. In this case mixtures of different precursors of oneor more elements may also be used.

Suitable precursors of silicon dioxide are alkoxides of silicon such as,for example, tetraethoxysilane, tetramethoxysilane.

Suitable precursors of aluminium oxide are lower alkoxides such astrimethoxyaluminium, triethoxyaluminium, tri-n-propoxyaluminium,tri-iso-propoxyaluminium, tri-sec-butoxyaluminium,tri-sec-butoxyaluminium, or tri-tert-butoxyaluminium or aluminiumalkoxides with chelating ligands such asdibutoxyaluminium-ethylacetoacetate.

Suitable precursors of titanium oxide are tetramethoxytitanium,tetraethoxytitanium, tetraisopropoxytitanium; suitable precursors ofzirconium oxide are tetraethoxyzirconium, tetra-tert-butoxyzirconium,tetra-n-butoxyzirconium, tetra-iso-propoxyzirconium. Suitablehydrolysable salts are for example titanium tetrachloride, organic saltssuch as aluminium acetylacetonate, zirconium acetylacetonate or thecorresponding mixed metal compounds and salts.

Suitable solvents are, for example, monohydric alcohols such asmethanol, ethanol, n-propanol, iso-propanol, n-butanol, 2-butanol,t-butanol, polyhydric alcohols such as glycol, 1,2-propanediol,1,3-propanediol, monofunctional or polyfunctional ketones such asacetone, 1,3-pentanedione(acetylacetone), cyclic or linear ethers withone to three oxygen atoms such as tetrahydrofuran, dioxan, diethylether, glycoldiethyl ether or diethyleneglycoldiethyl ether,ether-alcohols such as glycolmonomethyl ether, nitriles such asacetonitrile and benzonitrile and amides such as dimethylformamide.Alcohols, diketones and ether-alcohols are preferred. Obviously mixturesof solvents may also be used.

The solvents are used in amounts such that the molar ratio of alkoxideto solvent is 1:0.2 to 1:100.

Partially alkylated precursors R¹ _(x)M(OR²)_(y) may also be used in theprocess according to the invention, wherein M represents one of theelements mentioned under (i), (x+y) is the valency of the element and R¹and R², independently of each other, represent alkyl, aralkyl or arylgroups with 1 to 20 carbon atoms. The following may be mentioned by wayof example: methyltriethoxysilane, ethyltriethoxysilane.

Co-catalytic compounds which may be mentioned are one or more compoundsof elements from the groups 4, 5, 6, 7, 11, 12, 13, 14, the iron group(atomic numbers 26 to 28) or the rare-earth metals (atomic numbers 58 to71) in the periodic system of elements (IUPAC, new) with a total molarproportion of the components mentioned under (ii) of 0.1% to 99.9%,preferably 0.1% to 40%, in particular 0.5% to 20%, with respect to thetotal number of moles of the components mentioned under (i) and (ii),introduced into the catalyst, preferably Mn, Cu, Co, V, Nb, W, Zn, Ce,Mo, in particular Mn, Co, Cu, Mo, Ce, quite specifically Mn and/or Ce.

Suitable precursors of the co-catalytic metals are basically known, andthe following may be used for example: inorganic salts such as halides,oxides, nitrates, sulphates, carboxylates, salts of monofunctional orpolyfunctional organic C₂ to C₁₅ carboxylic acids such as acetates,cyclohexane butyrates, diketonates such as acetylacetonate, ethylhexanoate, alkoxides such as methoxides, ethoxides and isopropoxides andcomplex compounds which contain, for example, carbon monoxide, olefins,amines, nitriles, phosphines and halides, as well as mixed salts.

Heterometallic alkoxides of the formula [L_(m)M—(OR)₂—M′L_(n)′] are alsoknown and are described, for example, by Mehrotra et al in Mat. Res.Soc. Symp. Proc. 121 (1988) 81; D. C. Bradley et al in “MetalAlkoxides”, Academic Press, NY (1978); K. G. Caulton et al in Chem. Rev.90 (1990) 969.

Examples of compounds containing organic ligands which may be mentionedare: cerium(IV) isopropoxide, cerium(IV) methoxyethoxide, cerium(III)acetylacetonate, cobalt carbonylmethoxide, cobalt(II) acetylacetonate,cobalt(III) acetylacetonate, manganese(II) ethoxide, manganese(II)acetylacetonate, manganese(III) acetylacetonate, copper(II)2-ethylhexanoate, copper(II) ethoxide, copper(II) ethylacetoacetate,copper(II) acetylacetonate, niobium(V) ethoxide, molybdenum(V)ethoxide(dimolybdenum decaethoxide), molybdenum(VI)oxide-bisacetylacetonate, vanadium(IV) oxide-bisacetylacetonate(vanadylacetylacetonate), vanadium(III) acetylacetonate, vanadiumtri-isopropoxide oxide, vanadium tri-n-propoxide oxide, tungsten(VI)ethoxide, tungsten(V) ethoxide, tungsten(VI) phenoxide, zinc(II)acetylacetonate.

Suitable platinum metal compounds are, for example, the platinum metalcompounds and platinum metal-containing complex compounds described inEP-A 736 324. In, the examples mentioned, palladium was mentioned as theplatinum metal, but other platinum metals are also suitable such as Pt,Ir, Ru or Rh, Pd and Rh, however, are preferred, in particular Pd.Further examples of suitable platinum metal compounds are: Li₂(PdCl₄),Na₂(PdCl₄), K₂(PdCl₄), (NBu₄)₂(PdCl₄), Na₂(PdBr₄), K₂(PdBr₄),(NBu₄)₂(PdBr₄) (where Bu=n-butyl), platinum metal nitrates, acetates,propionates, butyrates, oxalates, carbonates, oxides, hydroxides,acetylacetonates and other compounds familiar to a person skilled in theart. Examples of olefin-containing, platinum metal complexes are[allylpalladium chloride] dimer [C₃H₅PdCl]₂, 1,5-cyclooctadienpalladiumdichloride C₈H₅PdCl₂; examples of phosphine-containing platinum metalcomplexes are 1,2-bis[(diphenylphosphino)ethane]palladium dichloridePd[(C₆H₅)₂PCH₂CH₂P(C₆H₅)₂]Cl₂, bis(triphenylphosphino)palladiumdichloride Pd[P(C₆H₅)₃]₂Cl₂; examples of amine-containing platinum metalcomplexes are diamminopalladium dibromide Pd(NH₃)₂Br₂, diamminopalladiumdichloride Pd(NH₃)₂Cl₂, tetraamminopalladiumtetrachloropalladate[Pd(NH₃)₄][PdCl₄]; examples of nitrile-containing platinum metalcomplexes are bis(acetonitrile)palladium dichloride Pd(CH₃CN)₂Cl₂,bis(benzonitrile)palladium dichloride Pd(C₆H₅CN)₂Cl₂; examples of carbonmonoxide-containing platinum metal complexes are tetrabutylammoniumtribromocarbonylpalladate (NBu₄)Pd(CO)Br₃ (where Bu=n-butyl) andtetrabutylammonium trichlorocarbonylpalladate (NBu₄)Pd(CO)Cl₃ (whereBu=n-butyl).

Catalysts according to the invention may be prepared in one or moresteps. In this case the platinum metal is introduced into the mixture,when preparing the mixed oxide, immediately or some time later. Modes ofoperation in which some of the amount of platinum metal is introducedinto the sol-gel process and the remainder is applied onto the mixedoxide at a later point are also possible.

When preparing catalysts according to the invention, a solution of theprecursors of (i) and (ii) are conventionally prepared in a suitablesolvent and hydrolysed with 1 to 20, preferably 1.5 to 10 moleequivalents of water, with respect to the total number of moles ofcompounds (i) and (ii). The water may be added in one or severalportions, pure, mixed with other solvents or together with theprecursors of (ii) or the platinum metal compounds dissolved therein.

According to the invention, one or more compounds of the platinum metals(atomic numbers 44 to 46 and 77 and 78) may be introduced to thecatalyst at different points in time in an amount of 0.01 to 20 wt. %,preferably 0.05 to 10 wt. % calculated as platinum metal and given withrespect to the total weight of the final catalyst.

In a preferred variant of the catalyst preparation, one or more platinummetal compounds are added before, during or after gelling to the mixtureof precursors of (i), (ii), the solvent, the water and optionally theacids or bases described above as a solution in a suitable solvent.

A soluble compound may be formed in situ from an insoluble precursor ofthe platinum metal compound by using a complexing agent or a furtherligand. In another preferred embodiment, the platinum metal compound isdissolved in the solvent used and added in that form. In a furtherpreferred embodiment, the platinum metal compound is added as solid orsolution to the pre-hydrolysed mixture.

During the hydrolysis procedure, acids or bases may be added in amountsof 0.1 to 200 mol. % with respect to the total number of moles ofcompounds (i) and (ii).

Suitable acids are, for example, hydrochloric acid, nitric acid,sulphuric acid, formic acid, acetic acid or higher carboxylic acids with3 to 8 carbon atoms. Di- and tricarboxylic acids with up to 8 carbonatoms are also suitable. Suitable bases are ammonia, quaternary ammoniumhydroxides, NR₄OH, in which the R groups, independently of each other,may be alkyl, aryl or aralkyl groups with 1 to 15 carbon atoms, e.g.tetramethyl-, tetraethyl-, tetrapropyl-, tetrabutyl-, tetrapentyl- ortetraphenylammonium hydroxide, or organic nitrogen bases such as amines,pyridines, guanidines. Preferred bases are ammonia and quaternaryammonium hydroxides. The acids and bases may be used as pure substances,as anhydrous solutions or as aqueous solutions.

When adding the individual components, efficient homogenisation of themixture should be ensured by using appropriate mixing devices such ase.g. stirrers or mixing nozzles.

If several compounds (i) and (ii) are hydrolysed, known techniques maybe applied in order to mutually adjust their reactivities. The followingmay be mentioned by way of example: pre-hydrolysis of one compound,chemical modification of one compound with a chelating agent, the use ofdifferent alkoxide groups in the compounds and hydrolysis at differenttemperatures, such as is described, for example, by D. A. Ward and E. I.Ko (Ind. Eng. Chem. Res. 34 (1995) 421).

Another suitable method for preparing mixtures according to theinvention from precursors of (i) and (ii) is the gelling of inorganicprecursors in aqueous systems, such as the preparation of silica gels byneutralising alkali metal silicates with strong acids. Additional steps,such as washing the gel, may be required in order to wash salts whichhave been formed out of the mixture. During the procedure described herethe precursor of (ii) or the platinum metal-containing compounds (iii)may be added, for example, to one of the components before mixing thealkali metal silicate and acid.

After gelling, it is advantageous to allow the gels to age attemperatures of 20 to 100° C., preferably 20 to 80° C., for a period ofat least 10 minutes. The upper limit to the ageing time is restrictedonly by economic factors and may be several weeks. Times between onehour and two weeks are preferred. Ageing may also be performed inseveral steps at different temperatures or at a temperature whichchanges slowly with time.

The gels are dried after they have been aged. Drying the gels may beperformed by a variety of methods, depending on the method ofpreparation, wherein drying has an effect on the internal surface areaand the pore volume of the materials.

Drying may take place on the one hand in air, under a vacuum or in astream of gas. Suitable gases for drying the gel in a gas stream arenitrogen, oxygen, carbon dioxide or noble gases or any mixture of thegases mentioned, preferably e.g. air. Gaseous hydrocarbons for examplealkanes such as methane, ethane, propane, butane, alkenes such asethene, propene, butene, butadiene and alkynes such as ethyne, propyne,etc in any composition may also be used. Drying is performed at 0 to300° C., preferably 20 to 250° C., in particular at 20 to 150° C. Thedrying time depends e.g. on the porosity of the gel and on the solventused. It is generally a few hours, for example 0.5 to 50 h, preferably 1to 40 h, in particular 1 to 30 h.

Another preferred method is drying under supercritical conditions suchas, for example, is described by G. M. Pajonk (Applied Catalysis 72(1991) 217) and Dutoit et al (J. Catal. 161 (1996) 651), and this leadsto gels with particularly high porosities. Carbon dioxide(T_(critical)=31° C., P_(critical)=73 bar) or alcohols above theircritical point (e.g. for ethanol T_(critical)=243° C., P_(critical)=63bar), for example, may be used. Drying may be performed, batchwise,continuously or part-continuously, optionally in the presence of anotherinert gas.

Reduction of the platinum metal may occasionally occur duringsupercritical drying with alcohols and this generally has a negativeeffect on the activity of the catalysts according to the invention. Inthese cases it is recommended that the catalysts be oxidised again afterdrying, for example by annealing at 200 to 800° C. in a stream of gaswhich contains oxygen, air, halogens or hydrogen halides.

Further methods of drying, particularly for gels prepared in aqueoussystems, are extractive and azeotropic drying such as are described, forexample, in U.S. Pat. Nos. 3,887,494, 3,900,457, 4,169,926, 4,152,503,4,436,883, 4,081,407.

After drying the dried mixed oxides may be calcined. Calcining may takeplace in air, under vacuum or in a gas stream. Suitable gases forcalcining mixed oxides in a gas stream are e.g. nitrogen, oxygen, carbondioxide or noble gases and any mixtures of the gases mentioned,preferably air. Calcining is performed at 100 to 800° C., preferably at100 to 700° C., in particular at 100 to 600° C. It may sometimes be ofadvantage if the composition of the gas is altered either suddenly orcontinuously during calcination. The calcining time is generally a fewhours, for example 0.5 to 50 h, preferably 1 to 40 h, in particular 1 to30 h.

It is also possible to apply the mixed oxides according to the inventionas a layer on other catalyst supports. Suitable support materials forthe application of a layer of metal mixed oxide are any industriallyconventional catalyst supports based on carbon, oxides of elements,carbides of elements or salts of elements in a variety of forms.Examples of carbon-containing supports are coke, graphite, carbon blackor active carbon. Examples of elemental oxide catalyst supports are SiO₂(natural or synthetic silicas, quartz), Al₂O₃ in a variety ofmodifications (α, γ, δ, η, θ), aluminas, natural and syntheticaluminosilicates (zeolites), TiO₂ (rutile, anatase), ZrO₂ or ZnO.Examples of elemental carbides and salts are SiC, AlPO₄, BaSO₄, CaCO₃,etc. They may be used either as chemically uniform pure substances or asmixtures. Powdered or particulate materials, or even monoliths, aresuitable for use according to the invention.

The invention also provides a process for preparing an organic carbonateby reacting an aromatic hydroxy compound with carbon monoxide and oxygenin the presence of the catalysts according to the invention, aquaternary ammonium or phosphonium salt and a base.

The organic carbonate prepared by the process according to the inventioncorresponds to the formula

R—O—CO—O—R  (I)

in which

R represents a substituted or non-substituted C₆ -C₁₂ aryl group,preferably a substituted or non-substituted phenyl group, in particulara non-substituted phenyl group.

Aromatic hydroxy compounds which may be used according to the inventioncorrespond to the formula

R—O—H  (II)

in which R is defined as above. Aromatic hydroxy compounds which can bereacted using the supported catalysts according to the invention are forexample phenol, o-, m- or p-cresol, o-, m- or p-chlorophenol, o-, m- orp-ethylphenol, o-, m- or p-propylphenol, o-, m- or p-methoxyphenol,2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol,2-naphthol or bisphenol-A, preferably phenol. The aromatic hydroxycompound may be substituted with one or two substituents such as a C₁-C₄alkyl group, a C₁-C₄ alkoxy group, fluorine, chlorine or bromine.

Catalysts according to the invention may be used as powders, mouldeditems or monoliths, preferably as powders or moulded items, and areseparated from the reaction mixture by e.g. filtration, sedimentation orcentrifuging.

Preparation of aromatic carbonates using supported catalysts accordingto the invention may be performed in a variety of ways. One possibilityis a batchwise process. In the event of a continuous mode of operationin either a counter-flow or parallel flow system, or in the tricklephase on a fixed bed catalyst, loads of 0.01 to 20 g of aromatic hydroxycompound per gram of supported catalyst per hour, preferably 0.05 to 10g of aromatic hydroxy compound per gram of supported catalyst per hour,in particular 0.1 to 5 g of aromatic hydroxy compound per gram ofsupported catalyst per hour are used. The supported catalyst used inbatchwise trials may be used repeatedly with the same feed materialswithout any purification. With a continuous mode of operation thesupported catalysts used may remain in the reactor for a long time. Acontinuous mode of operation in a single reactor or in a cascade ofreactors are preferably used when using supported catalysts according tothe invention.

If the supported catalyst is used as a powder, the stirred container tobe used for mixing the reaction components is fitted with stirrers whichcan be used for this purpose. When working with supported catalystpowders as a suspension in stirred vessels or bubble columns, amounts of0.001 to 50 wt. %, preferably 0.01 to 20 wt. %, in particular 0.1 to 10wt. % of supported catalyst powder, with respect to the amount ofaromatic hydroxy compound used, are used. In particularly preferredembodiments, the heterogeneous supported catalyst is used as mouldeditems fixed in place in stirred tanks, bubble columns, trickle phasereactors or cascades of these reactors, wherein different types ofreactors may also be used in combination in a cascade.

In the event that the catalyst is arranged as a fixed bed, the catalystis preferably used as moulded items, e.g. as spheres, cylinders, smallrods, hollow cylinders, rings, etc. If required, catalysts may bemodified further by extruding, making tablets, optionally adding furthercatalyst supports or binders such as SiO₂ or Al₂O₃, and calcining. Thepreparation and further processing of catalysts used according to theinvention are generally known to a person skilled in the art and arepart of the prior art.

In the process according to the invention any organic or inorganic basesor mixtures of these may be used. Examples of inorganic bases which maybe mentioned, without restricting the process according to theinvention, are alkali metal hydroxides and carbonates, carboxylates orother salts of weak acids and alkali metal salts of aromatic hydroxycompounds of the formula (II), e.g. alkali metal phenolates. Obviouslythe hydrates of alkali metal phenolates may also be used in the processaccording to the invention. An example of this type of hydrate which maybe mentioned here, without restricting the process according to theinvention, is sodium phenolate trihydrate. The amount of added water,however, is preferably such that a maximum of 5 moles of water are usedper mole of base. Higher amounts of water lead, inter alia, to poorerconversions and decomposition of the carbonates being formed. Examplesof organic bases which may be mentioned, without restricting the processaccording to the invention, are tertiary amines which may have C₆-C₁₀aryl, C₇-C₁₂ aralkyl and/or C₁-C₂₀ alkyl groups as organic groups, orpyridine bases or hydrogenated pyridine bases, for exampletriethylamine, tripropylamine, tributylamine, trioctylamine,benzyldimethylamine, dioctylbenzylamine, dimethylphenethylamine,1-dimethylamino-2-phenylpropane, pyridine, N-methylpiperidine,1,2,2,6,6,-pentamethylpiperidine. An alkali metal salt of an aromatichydroxy compound is preferably used as the base, in particular an alkalimetal salt of the aromatic hydroxy compound which is also being reactedto give the organic carbonate. This alkali metal salt may be a lithium,sodium, potassium, rubidium or caesium salt. Lithium, sodium andpotassium phenolate are preferably used, in particular sodium phenolate.

The base may be added to the reaction mixture as the pure compound insolid form or as molten material. In a further embodiment of theinvention the base is added to the reaction mixture as a solution whichcontains 0.1 to 80 wt. %, preferably 0.5 to 65 wt. %, in particular 1 to50 wt. % of the base. Solvents which may be used for this are eitheralcohols or phenols such as e.g. the phenol participating in thereaction or also inert solvents. Examples are those mentioned below foruse as reaction media. These solvents may be used individually or in anycombination with each other. Thus there is one embodiment of the processaccording to the invention, for example, in which the base is dissolvedin a molten phenol which has been diluted with a solvent. The base ispreferably dissolved in a molten aromatic hydroxy compound, inparticular in the molten aromatic hydroxy compound which is intended tobe reacted to give the organic carbonate. Quite specifically the base isdissolved in phenol. The base is added in an amount which does notdepend on the stoichiometry. The ratio of platinum metal, e.g.palladium, to base is preferably chosen so that 0.1 to 500, preferably0.3 to 200, in particular 0.9 to 130 equivalents of base, with respectto platinum metal, e.g. palladium, are used per mole of platinum metal,e.g. palladium.

The process according to the invention is preferably performed withoutusing a solvent. Obviously inert solvents may also be used. Examples ofsolvents which may be mentioned are dimethylacetamide,N-methylpyrrolidinone, dioxan, t-butanol, cumyl alcohol, isoamylalcohol, tetramethylurea, diethyleneglycol, halogenated hydrocarbons(e.g. chlorobenzene or dichlorobenzene) and ethers.

The quaternary salts used in the context of the present invention maybe, for example, ammonium or phosphonium salts substituted with organicgroups. Compounds suitable for use in the process according to theinvention are ammonium and phosphonium salts which contain, as organicgroups, C₆-C₁₀ aryl, C₇-C₁₂ aralkyl and/or C₁-C₂₀ alkyl groups and, asanion, a halide, tetrafluoroborate or hexafluorophosphate. Ammoniumsalts which are preferably used in the process according to theinvention contain, as organic groups, C₆-C₁₀ aryl, C₇-C₁₂ aralkyl and/orC₁-C₂₀ alkyl groups and, as anion, a halide, in particulartetrabutylammonium bromide. The amount of this type of quaternary saltis 0.1 to 50 wt. %, with respect to the weight of the reaction mixture.This amount is preferably 0.5 to 15 wt. %, in particular 1 to 5 wt. %.

The process according to the invention, preferably without a solvent, isperformed at 30 to 200° C., preferably 30 to 150° C., in particular 40to 120° C. at a pressure of 1 to 100 bar, preferably 2 to 50 bar, inparticular 5 to 25 bar.

EXAMPLES Comparison Example 1 In Accordance With EP-A 736 324

Preparing a Powdered Manganese Oxide Support

85 g of sodium hydroxide (2.125 mol) dissolved in 200 ml of water wereadded dropwise to a solution of 126 g of manganese(II) chloride (1 mol)in 500 ml of water. The precipitate obtained in this way was filteredunder suction, washed and dried. Then it was annealed for 3 h at 300° C.and for 2 h at 500° C.

Coating the Powdered Manganese Oxide with Palladium

300 ml of a solution of 50 g of sodium tetrachloropalladate(II) hydratecontaining 15% palladium in water were added to a slurry of 292.5 g ofmanganese dioxide powder in 1500 ml of water at room temperature. Themixture was adjusted to be alkaline using dilute caustic soda. Thesuspension was filtered under suction and dried at 100° C. Theheterogeneous catalyst contained 2.5% palladium on an MnO₂ support,calculated as metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

8.31 g of tetrabutylammonium bromide and 0.77 g of manganese(II)acetylacetonate dissolved in 450 g of phenol were introduced into anautoclave (1 litre) with a gas dispersion stirrer and condenser and witha cold trap connected in series. Then 4 g of the supported catalystdescribed above and 2.21 g of sodium phenolate dissolved in 50 g ofphenol were added. The pressure was then adjusted to 14 bars betintroducing a gaseous mixture of carbon monoxide and oxygen (95:5 vol.%). The amount of gaseous mixture was adjusted to 350 Nl/h. A sample waswithdrawn from the reaction mixture each hour and analysed gaschromatographically. The analyses showed that after 1 h 9.9% of diphenylcarbonate, after 2 h 15.2% of diphenyl carbonate and after 3 h 18.2% ofdiphenyl carbonate were present in the reaction mixture. 11.8 g of aphenol/water mixture had condensed in the cold trap.

Comparison Example 2 In Accordance with EP-A 736 325

Coating a Powdered Titanium Oioxide with Palladium and Manganese

300 ml of a solution of 40.5 g (0.16 mol) of manganese(II) nitratetetrahydrate in water were added to a slurry of 283.5 g of titaniumdioxide powder (Norton) in 1500 ml of water at room temperature. Themixture was then made alkaline with dilute caustic soda solution. Thesuspension was filtered under suction, washed with water, dried at 100°C. and annealed for 3 h at 300° C. The support, doped with manganese,was slurried in 1500 ml of water and then 300 ml of solution containing50 g of sodium tetrachloropalladate(II) hydrate containing 15% ofpalladium were added. The mixture was adjusted to be alkaline withdilute caustic soda solution. The suspension was filtered under suction,washed and dried at 100° C.

The catalyst contained 2.5% palladium and 3% manganese, each calculatedas the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in comparison example 1. The analysis showed thatafter 1 h 9.6% of diphenyl carbonate, after 2 h 16.1% diphenyl carbonateand after 3 h 21.0% diphenyl carbonate were present in the reactionmixture. 12.3 g of phenol/water mixture had condensed in the cold trap.

Example 1

Preparing a Si/Mn/Pd Co-gel

100 ml of tetraethoxysilane were mixed with a solution of 6.9 g ofmanganese(III) acetylacetonate and 1.24 g of palladium(II)acetylacetonate in 200 ml of ethanol and then 36 ml of 25.7% strengthaqueous hydrochloric acid were added over the course of 18 minutes withstirring. The mixture was allowed to stand for 6 days at roomtemperature and then dried for 2 days at 40° C. in a vacuum dryingcabinet. The solid obtained in this way was milled and annealed for 3 hat 300° C. in a stream of air.

The catalyst contained 1.5% palladium and 3.0% manganese, eachcalculated as the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in comparison example 1, but with the differencethat 6.7 g of catalyst were used. Analysis showed that after 1 h 9.2%diphenyl carbonate, after 2 h 17.8% diphenyl carbonate and after 3 h24.4% diphenyl carbonate were present in the reaction mixture. 15.0 g ofa phenol/water mixture had condensed in the cold trap.

Example 2

Preparing a Si/Mn/Pd Co-gel

The catalyst was prepared in the same way as described in example 1 withthe difference that 13.8 g of manganese(III) acetylacetonate, 2.48 g ofpalladium(II) acetylacetonate and 300 ml of ethanol were used.

The catalyst contained 3.0% palladium and 6.0% manganese, eachcalculated as the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in example 1, but with the difference that 3.3 gof catalyst were used. Analysis showed that after 1 h 11.6% diphenylcarbonate, after 2 h 21.4% diphenyl carbonate and after 3 h 27.0%diphenyl carbonate were present in the reaction mixture. 16.5 g of aphenol/water mixture had condensed in the cold trap.

Example 3

Preparing a Si/Mn/Pd Co-gel

100 ml of tetraethoxysilane were mixed with a solution of 6.9 g ofmanganese(III) acetylacetonate in 200 ml of ethanol and then a solutionof 1.24 g of potassium tetrachloropalladate in 36 ml of 25.7% strengthaqueous hydrochloric acid were added over the course of 18 minutes withstirring. The mixture was allowed to stand at 40° C. for 3 days and thendried for 2 days at 40° C. in a vacuum drying cabinet. The solidobtained in this way was milled and annealed for 3 h at 300° C. in astream of air.

The catalyst contained 1.5% palladium and 6% manganese, each calculatedas the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in example 1. Analysis showed that after 1 h 11.4%diphenyl carbonate, after 2 h 19.2% diphenyl carbonate and after 3 h24.2% diphenyl carbonate were present in the reaction mixture. 13.9 g ofa phenol/water mixture had condensed in the cold trap.

Example 4

Preparing a Si/Mn/Pd Co-gel

The catalyst was prepared as described in example 1 except that amixture of 17 ml of glacial acetic acid and 30 ml of water were used forhydrolysis instead of hydrochloric acid.

The catalyst contained 1.5% palladium and 6% manganese, each calculatedas the metal.

Use of the Supported Catalyst to Prepare Diphenyl Carbonate

The supported catalyst was used to prepare diphenyl carbonate in thesame way as described in example 1. Analysis showed that after 1 h 13.4%diphenyl carbonate, after 2 h 19.6% diphenyl carbonate and after 3 h24.6% diphenyl carbonate were present in the reaction mixture. 15.1 g ofa phenol/water mixture had condensed in the cold trap.

What is claimed is:
 1. A process for preparing an organic carbonate comprising: (I) preparing a catalyst by a process comprising: (a) providing a sol-gel comprising, (i) a first metal oxide selected from the group consisting of silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and mixtures thereof, (ii) a second metal oxide selected from the group consisting of metal oxides of the elements of groups 4, 5, 6, 7, 11, 12, 13, 14, the iron group (atomic numbers 26 to 28), the rare-earth metals (atomic numbers 58 to 71) and mixtures thereof, and (iii) a metal selected from the group consisting of platinum metals, compounds of platinum metals (atomic numbers 44 to 46 and 77 and 78) and mixtures thereof, said metal being present in an amount of 0.01 to 15 wt. %, calculated as platinum metal with respect to the total weight of said catalyst, said first metal oxide (i), said second metal oxide (ii) and said metal (iii) each being formed independently from suitable precursors, (b) aging said sol-gel to obtain an aged sol-gel; and (c) drying said aged sol-gel to obtain said catalyst; and (II) reacting an aromatic hydroxy compound with carbon monoxide and oxygen in the presence of said catalyst, a quaternary ammonium or phosphonium salt and a base.
 2. The process of claim 1 wherein the catalyst obtained in step (c) is then annealed.
 3. The process of claim 1 wherein said second metal oxide (ii) is selected from the group consisting of oxides of the elements manganese, copper, cobalt, vanadium, niobium, tungsten, zing, cerium and mixtures thereof.
 4. The process of claim 1 wherein the platinum metal of said metal (iii) is selected from the group consisting of platinum, palladium, iridium, ruthenium, rhodium and mixtures thereof.
 5. The process of claim 1 wherein the platinum metal compound of said metal (iii) is selected from the group consisting of Li₂(PdCl₄), Na₂(PdCl₄), K₂(PdCl₄), (n-butyl)₂(PdCl₄), Na₂(PdBr₄), K₂(PdBr₄), allylpalladium chloride dimer, 1,5-cyclooctadienpalladium dichloride, 1,2-bis((diphenylphosphino)ethane)palladium, bis(triphenylphosphino)palladium, diamminopalladium dibromide, diamminopalladium dichloride, tetraamminopalladiumtetrachloropalladate, bis(acetonitrile)palladium dichloride, bis(benzonitrile)palladium dichloride, tetrabutylammonium tribromocarbonylpalladate, tetrabutylammonium trichlorocarbonylpalladate and mixtures thereof.
 6. The process of claim 1 wherein said first metal oxide (i) is silicon dioxide; said second metal oxide (ii) is manganese oxide; and said metal (iii) is selected from palladium metal and compounds of palladium metal.
 7. The process of claim 1 wherein said base is an inorganic base selected from the group consisting of alkali metal hydroxides and alkali metal salts of aromatic hydroxy compounds.
 8. The process of claim 1 wherein said base is an organic base selected from the group consisting of: tertiary amines having organic groups selected from C₆-C₁₀ aryl, C₇-C₁₂ aralkyl, C₁-C₂₀ alkyl and combinations thereof; pyridine bases; and hydrogenated pyridine bases.
 9. The process of claim 8 wherein said organic base is selected from the group consisting of triethylamine, tripropylamine, tributylamine, trioctylamine, benzyldimethylamine, dioctylbenzylamine, dimethylphenethylamine, 1-dimethylamino-2-phenylpropane, pyridine and N-methylpiperidine, 1,2,3,6,6-pentamethylpiperidine.
 10. The process of claim 1 wherein said quaternary ammonium salt and said quaternary phosphonium salt each independently have: organic groups selected from C₆-C₁₀ aryl, C₇-C₁₂ aralkyl, C₁-C₂₀ alkyl and combinations thereof; and anion groups selected from halide, tetrafluoroborate and hexafluorophosphate.
 11. The process of claim 1 wherein said organic carbonate is represented by the following formula, R—O—C(O)—O—R wherein R is a substituted or non-substituted C₆-C₁₂ aryl group, and said aromatic hydroxy compound is represented by the following formula, R—OH wherein R is as described above.
 12. The process of claim 11 wherein said aromatic hydroxy compound is selected from the group consisting of m-cresol, p-cresol, o-chlorophenol, phenol, m-chlorophenol, p-chlorophenol, o-ethylphenol, m-ethylphenol, p-ethylphenol, o-propylphenol, m-propylphenol, p-propylphenol, o-methoxyphenol, m-methoxyphenol, p-methoxyphenol, 2,6-dimethylphenol, 2,4-dimethylphenol, 3,4-dimethylphenol, 1-naphthol, 2-naphthol, 4,4′-isopropylidenediphenol and mixtures thereof. 